Such a method is known from the publication DE 101 38 217.0. Therein, information packets are transmitted between a base station and a transponder. The information packets consist of a header section and a middle section with a data region. In the middle section, the data of the data region are encoded with the identifications allocated to the logic values of the information symbols in the header section. A disadvantage of the method is that disturbing or noisy interferences reduce the reliability of the data transmission in the communication due to reflections and/or absorptions when utilized in the range of UHF and higher. For the correction of the read errors, the entire data packet must be transmitted.
A further method is known from the publication EP 473,569 B1. Therein, digital data are exchanged between a base station and a passive transponder by means of an amplitude modulated carrier wave. The individual bits of a data word consist of a time span or interval in which the electromagnetic field is switched on and a time span or interval in which the electromagnetic field (field gap or notch) is switched off, whereby the field gap serves as a separator between two successive bits. The logic value of the bits is determined by the length of the time in which the electromagnetic field is switched on. The fixed time amount of the field gap is summed or additionally counted for the total time for the representation of the individual bits. Furthermore, in the passive system, the energy for the transponder is acquired out of the carrier field by means of absorption modulation.
A further method is known from the publication EP 0,777,191 A1. Therein, data are transmitted by means of a PWM modulated carrier wave, whereby the logic values of the bits are represented by various different time lengths, and the carrier field is briefly switched on for the separation of the individual bits at the end of a time interval in the so-called forward link. Furthermore, various different encoding methods for the transmission of digital data are known from Finkenzeller, “RFID Handbuch” (“RFID Handbook”), especially page 106 et seq. and the publication U.S. Pat. No. 3,560,947.
Due to the increasing security or safety demands, a plurality of information packets must be modulated onto a carrier wave in ever-shorter time spans or intervals. Preferably an amplitude modulation (ASK) is used for the modulation. In order to achieve a higher data transmission rate and a higher transmission distance or range, carrier frequencies in the range of UHF and microwaves are being increasingly utilized in the field of the transponders. The basic foundation of the bi-directional data transmission between transponder and base station is formed by a data protocol, which, among other things, sets or fixes the number of the information symbols, such as for example the logic values per data bit, and also defines the identification of the individual symbols. Especially in the UHF range, read errors arise in the data transmission due to change or variation of the transmission conditions as a result of reflections and the constructive and destructive interferences associated therewith. Because this results in a repeated transmission of the data word, the effective data transmission rate is considerably reduced.
A disadvantage of the previous methods is that the effective data transmission rate is reduced due to the transmission errors especially in the range of very high frequencies due to the fluctuating transmission conditions. This reduction of the data transmission rate is noticeable in a disturbing or interfering manner in time-critical applications. It is an object of the present invention to set forth a method for the transmission of data, which increases the reliability of the data transmission and can be carried out in a simple and economical manner.